The present invention relates to a technology for increasing the storage capacity of a magnetic disk drive that adopts a load/unload method, and more particularly to a technology for writing data without decreasing the reliability and performance for a load/unload area.
There are magnetic disk drives adopting the load/unload method that uses a ramp located in the vicinity of the outer circumference of a magnetic disk as a region into which a head/slider is retracted while the magnetic disk is not accessed. In the vicinity of the outer circumference of the magnetic disk, a load/unload area is defined on a recording surface as an area used when the head/slider is loaded. A data area, which is an area to which user data is written, is defined on the inner circumferential side of the load/unload area.
The load/unload area also includes an area to which servo data is written. Therefore, if the firmware is changed, it is possible to write data to this area in the same manner as that in the case of the data area from the viewpoint of a format of the magnetic disk. However, while the head/slider which is loaded from the ramp to the magnetic disk is in the load/unload area, the floating posture of the head/slider is unstable. Accordingly, there is a higher possibility that the head/slider will touch the recording surface of the magnetic disk, causing damage to the magnetic disk. For this reason, in order to use the load/unload area as a recording area of user data, it is necessary to take the reliability of data into consideration.
Patent document 1 (U.S. Pat. No. 5,633,767) states that data is written to a load/unload area of a disk drive. Patent document 1 also states that a magnetic disk drive usually includes error recovery procedure and that if the performance decreases, data is reallocated to an alternate track or cylinder. Moreover, according to patent document 1, even if an error rate of data written to the load/unload area slowly increases or irregularly increases, no problem arises. However, if the error rate exceeds a threshold value, there is a fear of causing a serious failure of the magnetic disk drive.
Patent document 2 (U.S. Pat. No. 6,480,361) states that in order to prevent a transducer from touching written data at the time of loading, it is necessary to form, in the vicinity of the outer circumference of a magnetic disk, a tolerance band to which data is not written. Patent document 2 discloses a technology in which a movable ramp mechanism is provided to extend, in the vicinity of the outer circumference of the disk, an available area to which data can be written. Patent document 3 (Japanese Patent Laid-open No. 2005-085322) discloses a technology for using a load/unload area as an area to which data is written by forming an arc-shaped load/unload zone in the circumferential direction of the load/unload area, and by writing data to an area other than the load/unload zone.